We describe a novel approach to evaluating the respiratory toxicity of chemicals in the free-living nematode Caenorhabditis elegans. Using DOX-96KT, a general purpose, multi-channel dissolved oxygen (DO) measuring system, we measured the DO concentration in culture media containing C. elegans exposed to chemicals to assay for respiratory toxicity. The current value, which is an index of the dissolved oxygen concentration in culture media, was measured every 10 sec for 30 min at 24°C. We focused on the respiration levels of the exposed worms between 500 and 1800 sec. This method produces results that are similar to the computer tracking system measuring behavioral toxicity. Since it can do multiple dilution series tests at a given time, it is useful for concentration-activity correlation studies. This novel technique is not only an alternative to the computer tracking system for measuring behavioral toxicity but also a rapid sublethal toxicity test for chemical hazard assessment.